1. Field of Invention
This invention is in the field of analog to digital encoding and auto correction for the reduction of comparator errors used therein.
2. Description of the Related Art
Signal conversion from one format to another is an essential part of today""s electronic systems. For example, analog signals are typically converted from an analog format to a digital format to facilitate certain operations. This analog to digital conversion (A/D) generates a digital representation of the analog signal. The digital representation facilitates further processing of the original analog signal using digital components such as memories and processors. Using digital means of processing is desirable as it facilitates mathematical operations while avoiding the limitations inherent in an analog environment.
For effective signal processing, the A/D conversion process needs to maintain fidelity to the analog signal. That is, the digital representation of the analog signal accurately represents the original analog signal converted into digital format. The desire for fidelity in converting between analog and digital representation has created various mechanisms to avoid limitations inherent in a digital representation. For example, where analog signals have a wide dynamic range, the conversion to the digital format is allocated in amplitude intervals to allow relatively accurate representation of the analog signal using a limited number of digital bits. This method for converting wide dynamic range analog signals into digital bits assigns linear amplitude intervals for conversion along the overall analog signal amplitude. This method, referred to as piece wise linear conversion, generates a digital output for each interval. The intervals may be assigned to portions of the maximum voltage of the analog signal so that the result is a non-linear conversion to digital, typically compressing the wide dynamic range of the amplitude of the analog signal into the available number of bits of the digital format. If errors are minimized, the inverse of the non-linear transfer function can be used at a digital to analog converter to restore the wide dynamic range analog signal from its digital representation.
However, in choosing a piece wise linear conversion method errors are encountered, typically at the decoder, or receiving end. The decoder may mis-identify the location of the transitions between the different linear segments of the piece wise linear conversion intervals. This source of error introduces discontinuities between the adjoining segments of the piece wise linear function, generating errors in the reconstructed analog signal.
Conversion errors of the prior art are reduced by a piece wise linear analog to digital converter. The analog to digital converter operates between a minimum voltage and a maximum voltage and uses one or more comparators to generate one or more digital bits, each of the digital bits representative of a conversion voltage. A first voltage interval is allocated for linear analog to digital conversion. This first voltage interval extends from the minimum voltage to an intermediate voltage, where the intermediate voltage is less than the maximum voltage. A second voltage interval extends from the intermediate voltage to the maximum voltage.
An error correcting band is encoded in the analog signal between the first voltage interval and the second voltage interval.
Each of the comparators has a sensing level. The error correcting band is centered with respect to one of the sensing levels, the sensing level located at the intermediate voltage. The error correcting band extends over a correcting voltage. The correcting voltage a fraction of the conversion voltage.